1. Field of the Invention
The present invention relates to a recording sheet for an ink jet printer, and in particular, relates to a recording sheet for an ink jet printer, in which printing density is high; printing is vivid; ink absorptivity is superior; light resistance, ozone resistance, and moisture resistance are superior; and ink is quickly absorbed. The recording sheet satisfies future high speed printing technique requirements.
2. Description of the Related Art
The use of ink jet printers has continued to increase in recent years because they have characteristics such as vividness of recorded images, quiet operation, ease of coloring, and the like. In order to prevent the jet nozzle thereof from being blocked due to drying of ink, an ink which is difficult to dry must be used in the ink jet printers. As ink having this property, water-soluble ink which is dissolved or dispersed with adhesive, dye, solvent, additives, or the like, in water, is generally employed. However, a symbol or an image formed on a recording sheet by employing the water-soluble ink is inferior to that of printed matter or silver halide photographs due to the use of pigment-type inks, from the viewpoint of light resistance, ozone resistance, and moisture resistance.
In recent years, as ink jet printers become inexpensive and printing images having high vividness and colorfulness are easily obtained, the requirements for ink absorptivity and color reproducibility have increased, and further improvement of printing density or further vivid coloring is thereby desired. In addition, the requirements for shelf life such as light resistance, ozone resistance, etc., are becoming severe. Therefore, completely satisfying these various requirements is an essential goal for recording sheets for ink jet printers.
In consideration of this present situation, improvements of recording sheets for ink jet printers have been researched. A method for improving color reproducibility and ink absorptivity by adding amino acids, for example, typified by Japanese Patent Applications, Publications No. 8-295075 and No. 7-276791, have been proposed. In addition, a method for improving light resistance of the images by using additives such as polyphenol, etc., has also been proposed. However, it has been confirmed that the addition of only these amino acids produces disadvantages such as decrease of vividness of images, reduction of light resistance and moisture resistance, etc., and that the addition of polyphenol produces yellowing over time, and all of the properties of printing density, vividness of images, and shelf life have not yet been sufficiently improved.
It is an object of the present invention to provide a recording sheet for an ink jet printer which can improve recording properties such as vividness of images, printing density, etc., and shelf life such as light resistance of images, ozone resistance, etc.
According to the results that the inventors have obtained from various research with regard to a recording sheet for an ink jet printer, the recording properties such as vividness of images, printing density, etc., and the shelf life such as light resistance of images, ozone resistance, etc., are improved very effectively by including an oligosaccharide and divalent metallic salt in the recording sheet for an ink jet printer, and the inventors have thereby attained the present invention. In other words, the recording sheet for an ink jet printer according to the present invention is characterized in that an ink receiving layer is provided on at least one side of a base material, and at least one of the ink receiving layer and the base material includes an oligosaccharide and divalent metallic salt. Furthermore, in the recording sheet for an ink jet printer of the present invention, it is preferable that the oligosaccharide and the divalent metallic salt be included in the ink receiving layer. In the following, the preferred embodiments according to the present invention will be explained in detail.
The recording sheet for an ink jet printer according to the present invention is a laminated sheet in which at least one ink receiving layer is provided on at least one surface of a base material by a providing means such as a coating method, or the like. The ink receiving layer may be provided as two layers or more. In the following, materials which compose the base material and the ink receiving layer will be explained. The recording sheet for an ink jet printer of the present invention can exhibit superior recording properties and shelf life properties if the oligosaccharide and the divalent metallic salt are included not only in the ink receiving layer but also in any layer of the recording sheet for an ink jet printer; however, in the following, an embodiment which includes the oligosaccharide and the divalent metallic salt in the ink receiving layer will be explained.
(1) Base Material
As a base material provided for coating an ink receiving layer thereon according to the present invention, a base paper in which is mixed wood pulp such as chemical pulp such as LBKP, NBKP, or the like; mechanical pulp such as GP, PGW, RMP, TMP, CTMP, CMP, CGP, or the like; recycled pulp such as DIP, or the like; etc.; or synthetic fiber pulp such as that of polyethylene fiber, or lo the like, as a primary component, with pigment, sizing agent, fixer, yield improving agent, strengthening agent, or the like, alone or in combination, as necessary, and which is produced by using any type of apparatus such as a fourdrinier paper machine, cylinder paper machine, twin wire paper machine, or the like; can be preferably employed. In addition, a base paper provided with starch, polyvinyl alcohol, or the like using a size press; and a coated paper such as art paper, coated paper, cast coat paper, or the like, in which a coat layer is provided on these base papers, can be preferably employed. These base papers and coated papers may support an ink receiving layer directly, and in order to control smoothness of the surface thereof, a calender apparatus may be used such as a machine calender, TG calender, soft calender, or the like, before coating the ink receiving layer.
As a base material, a polyolefin resin layer may be provided on the surface of the above-described base paper, and film material of synthetic resin such as polyethylene, polypropylene, polyester, nylon, rayon, polyurethane, or the like; film material comprised of a mixture with these; and fiber-formed sheets of these synthetic resins may be employed.
(2) Ink Receiving Layer
The ink receiving layer in the recording sheet for an ink jet printer of the present invention is formed by a primary component comprising pigment and binder resin and various additives which are added as necessary, and in the present invention, it is preferable that the ink receiving layer contain divalent metallic salt in addition to oligosaccharide, so as to attain superior light resistance and ozone gas resistance. In the following, materials which can be employed in the ink receiving layer will be explained.
(A) Pigment
In an ink receiving layer according to the present invention, generally used pigments which are insoluble or slightly soluble in water can be employed alone or in combination. For example, a white inorganic pigment such as precipitated calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, diatomite, calcium silicate, magnesium silicate, synthetic amorphous silica, colloidal silica, colloidal alumina, pseudo-boehmite, aluminum hydroxide, alumina, lithopone, zeolite, hydrolytic halloysite, magnesium carbonate, magnesium hydroxide, or the like; an organic pigment such as styrene-type plastic pigment, acrylic-type plastic pigment, polyethylene, microcapsules, urea resin, melamine resin, or the like, etc., can be employed.
Of these pigments, as a white pigment which is a primary component contained in an ink receiving layer, a porous inorganic pigment is preferable since drying properties and absorptivity of an ink for an ink jet printer is excellent. For example, porous synthetic amorphous silica, porous magnesium carbonate, porous alumina, or the like, are preferably employed. Of these, since both printing quality and shelf life are satisfied in the present invention, the precipitation type or the gel type of porous synthetic amorphous silica with a specific surface area of about 200 to 600 g/m2 can be preferably employed.
(B) Binder Resin
As binder resin contained in an ink receiving layer according to the present invention, polyvinyl alcohol, silyl modified polyvinyl alcohol, vinyl acetate, oxidized starch, etherificated starch, casein, gelatin, soybean protein; cellulosic derivative such as carboxymethyl cellulose, hydroxyethyl cellulose, or the like; conjugate diene type copolymer latex such as maleic anhydride resin, styrene-butadiene type copolymer, methylmethacrylate-butadiene copolymer, or the like; acrylic type polymer latex such as (meth)acrylic acid ester polymer, (meth)acrylic acid ester copolymer, or the like; vinylic type polymer latex such as ethylene-vinylacetate copolymer, or the like; functional group modified polymer latex comprised of monomers including functional groups such as a carboxy group, or the like of all types of these polymers; water-soluble adhesive consisting of thermosetting synthetic resin such as melamine resin, urea resin, or the like; synthetic resin type adhesive such as polymethylmethacrylate, polyurethane resin, unsaturated polyester resin, vinylchloride-vinylacetate copolymer, polyvinylbutyral resin, alkyd resin, or the like, can be preferably employed. These can be employed alone or in combination. The compounding ratio of the pigment to the binder resin in the ink receiving layer in the present invention is preferably 1:1 to 15:1, and is more preferably 2:1 to 10:1.
(C) Oligosaccharide
As an oligosaccharide contained in the recording sheet for an ink jet printing of the present invention, maltooligosaccharide and isomaltooligosaccharide can be employed. In the following, maltooligosaccharide and isomaltooligosaccharide will be explained.
The maltooligosaccharide in the present invention refers to carbohydrates having a polymerization degree of 2 or more in which units consisting of glucose are combined by xcex11xe2x86x924 bond. Specifically, maltose (glucose polymerization degree of 2) in which two glucose molecules are combined, maltotriose having a polymerization degree of 3, maltotetraose having a polymerization degree of 4, maltopentaose having a polymerization degree of 5, maltohexaose having a polymerization degree of 6, maltoheptaose having a polymerization degree of 7, etc., can be mentioned. In the present invention, maltooligosaccharide having a glucose polymerization degree of 2 to 10 is preferably employed, and in particular, maltooligosaccharide having a glucose polymerization degree of 2 to 7 is preferably employed, because effects such as recording property, light resistance and ozone resistance are superior. When glucose having a polymerization degree of 1 which is a unit is employed, vividness of images and ozone resistance are inferior, and the object of the present invention is not attained. In contrast, when maltooligosaccharide having a polymerization degree over 10 is employed, there is a problem in that light resistance and vividness of images are deteriorated.
The isomaltooligosaccharide in the present invention refers to carbohydrates in which units consisting of glucose are combined by xcex11xe2x86x926 bond, and in addition, carbohydrates having a bond other than the xcex11xe2x86x924 bond. Specifically, as an isomaltooligosaccharide having xcex11xe2x86x926 bond, isomaltose in which two glucose molecules are combined (glucose polymerization degree of 2), isomaltotriose and panose having a polymerization degree of 3, etc., can be mentioned, and as an isomaltooligosaccharide having a bond other than the xcex11xe2x86x924 bond, gentiooligosaccharide having xcex21xe2x86x926 bond such as gentose, etc., nigerooligosaccharide having xcex11xe2x86x923 bond such as nigerose, etc., trehalose and glucosylsucrose, having xcex11xe2x86x921 bond, etc., can be mentioned. In the present invention, isomaltooligosaccharide having a glucose polymerization degree of 2 to 5 is preferably employed because effects such as recording characteristics, light resistance and ozone resistance are superior. When glucose having a polymerization degree of 1 which is a unit is employed, vividness of images and ozone resistance are inferior, and the object of the present invention is not attained. In contrast, when isomaltooligosaccharide having a polymerization degree over 5 is employed, there is a problem in that light resistance and vividness of images are deteriorated.
The oligosaccharides employed in the present invention can be prepared by heating starch in dilute acid to hydrolyze glucoside bonds, by amylolytic enzymes such as amylase to hydrolyze starch or amylose, or by transglycoside enzymes. The starch to be a raw material of the oligosaccharide can be optionally chosen from grain starch made from rice, corn, etc., and tuber starch made from potato, cassava, etc. Since the oligosaccharide prepared by the above procedures contains oligosaccharides having various degrees of polymerization, a separation and purification process is required in order to obtain oligosaccharide having a pure single degree of polymerization. However, a purification process for fractionating or isolating by using a gel filtration chromatography, etc., is desired in order to obtain oligosaccharide having a pure single degree of polymerization because oligosaccharides having a high degree of polymerization are difficult to crystallize.
As an oligosaccharides employed in the present invention, oligosaccharides having a pure single degree of polymerization obtained by the above purification can be employed, and in addition, a maltooligosaccharide mixture of maltooligosaccharides having a glucose polymerization degree of 2 or more and glucose which is obtained by, for example, carrying out saccharification reactions on starches using xcex2-amylase and debranching enzyme, can also be employed. In the case in which such an oligosaccharide mixture having different degrees of glucose polymerization is employed, a maltooligosaccharide mixture comprising maltooligosaccharides having a glucose polymerization degree of 2 to 10 as a primary component is preferred, and of those, a maltooligosaccharide mixture in which the content of the maltooligosaccharides having a glucose polymerization degree of 2 to 7 is 50% by weight or more is preferred, and a maltooligosaccharide mixture in which the content is 70% by weight or more is even more preferable. Furthermore, an isomaltooligosaccharide mixture comprising isomaltooligosaccharides having a glucose polymerization degree of 2 to 5 as the primary component is preferred.
The content of the above oligosaccharide may be an optional proportion for total solids of the ink receiving layer, and it is preferably 0.5 to 30.0% by weight and is more preferably 5.0 to 20.0% by weight. When the content is under 0.5% by weight, the improvement effects such as ozone resistance of images, etc., are insufficient, and in contrast, when the content exceeds 30.0% by weight, ozone resistance and light resistance are sufficiently improved; however, further improvement is not obtained and there are problems in that water resistance and ink absorbability is decreased and in that coating film strength of the ink receiving layer is deteriorated. In addition, in the case in which these oligosaccharides are contained in the base material, they can be coated at about 0.2 to 15.0 g/m2 by a size press, etc., or they can be added to the base material at 0.5 to 30.0% by weight.
(D) Divalent Metallic Salt
In the recording sheet for an ink jet printer of the present invention, by using a divalent metallic salt with an oligosaccharide, a synergistic effect can be obtained in which the effect due to addition of the oligosaccharide is further exhibited while superior ink absorbability is retained. In this case, the divalent metallic salt refers to a compound which produces a positive divalent metal ion when it is ionized by dissolving in water, etc. The divalent salt can be optionally selected, and specifically, a halide, hexafluorosilylate, sulfate, thiosulfate, acetate, phosphate, chloric acid salt, or nitric acid salt of typical elements such as zinc, magnesium, calcium, strontium, barium, gallium, indium, thallium, germanium, tin, lead, bismuth, etc., can be mentioned. Of these metals, zinc, manganese, and chromium, are preferred, and of these salts, chloride, sulfate, and acetate, are preferred, and in particular, compounds which combine these can be preferably employed. Specifically, zinc chloride, zinc sulfate, zinc acetate, magnesium chloride, magnesium sulfate, magnesium acetate, calcium chloride, calcium sulfate, calcium acetate, can be mentioned.
The content of the metallic salt relative to the total solid content of the ink receiving layer may be at any ratio, and preferably ranges from 1.0 to 40.0% by weight, and more preferably ranges from 5.0 to 20.0% by weight. When the content is less than 1.0% by weight, although the effects of recording properties, light resistance of images, and ozone resistance are confirmed, they are not sufficient. In contrast, when the content exceeds 40.0% by weight, light resistance and ozone resistance are sufficiently improved; however, further improvement is not anticipated, and there are problems in that water resistance and moisture resistance are decreased or in that strength of a coating film of the ink receiving layer is reduced. Furthermore, there is a problem in that recording quality of the ink jet recording is deteriorated. In addition, in order to achieve vivid printing images, the content range of the metallic salt is preferably 5.0 to 40.0% by weight to pigment, and is more preferably 10.0 to 20.0% by weight.
(E) Other Additives
Furthermore, as other additives added to the ink receiving layer, cationic dye fixing agent, pigment dispersing agent, thickener, fluidity improving agent, defoaming agent, foam inhibitor, surface lubricant, foaming agent, penetrating agent, color dye, color pigment, fluorescent brightening agent, UV absorber, antioxidant, antiseptics, water resistance agent, hardening agent, or the like, can be blended in an appropriate ratio as necessary.
Of these additives, in particular, it is preferrable that the cationic dye fixing agent be added since it cooperates with the oligosaccharide having an effect of improving light resistance and ozone resistance. As a cationic dye fixing agent, various cationic polymers can be employed, and specifically, polyethyleneimine salt, polyvinylamine salt, acrylamide copolymer, condensation polymer salt of secondary amine and epihalohydrin, etc., can be employed. In order to obtain all of the effects of superior ozone resistance, light resistance, and water resistance and to improve the effectiveness thereof, the solid content of the cationic dye fixing agent content and the oligosaccharide content in the ink receiving layer is preferably 2:1 to 1:4 and is more preferably 3:2 to 1:2.
The composition of the ink receiving layer according to the present invention is not limited to the above-described materials. In order to satisfy various properties such as light resistance or ozone resistance and to solve production problems such as adhesion to the base material, pigments falling off in the layer in the cutting process, or the like, the solid content of each material in the ink receiving layer is most preferably 30.0 to 60.0% by weight of pigment, 20.0 to 40.0% by weight of binder resin, 5.0 to 20.0% by weight of oligosaccharide, and 5.0 to 20.0% by weight of divalent metallic salt.
The ink receiving layer is formed on a base material by coating the coating material which was prepared by dissolving or dispersing in water or a suitable solvent, using various kinds of apparatuses such as a blade coater, roll coater, air knife coater, bar coater, rod blade coater, size press, or the like on-machine or off-machine as appropriate. The coating weight of the ink receiving layer in the one layer type is preferably 5.0 to 30.0 g/m2, and is more preferably 5.0 to 20.0 g/m2. In the case of the two layer type in which is provided the first ink receiving layer on a base material and in which is provided the second ink receiving layer on the first ink receiving layer, the coating weight of the first ink receiving layer is preferably 5.0 to 30.0 g/m2, and is more preferably 5.0 to 20.0 g/m2. In addition, the coating weight of the second ink receiving layer is preferably 5.0 to 15.0 g/m2, and is more preferably 5.0 to 10.0 g/m2. In the case in which the coating weight is below the above range, excellent ink absorptivity or fixativity is seldom obtained. In the case in which it is over the above range, problems such as powdering of the layer, decrease in productivity, increase in cost, or the like occurs. In particular, in the case in which the coating weight of the second ink receiving layer is more than 15.0 g/m2, it is difficult for the ink to pass through to the second ink receiving layer, thereby causing blurring of ink, so that vividness of images is impaired. Therefore, it is preferred that the coating weight of the ink receiving layer be controlled according to the number of the ink receiving layers provided.
In the case in which two or more ink receiving layers are provided, the oligosaccharide may be contained in any of the ink receiving layers, or it may be contained in some of the ink receiving layers. In the case in which the oligosaccharide is contained in some ink receiving layers, in order to reduce the concentration difference between the layers, the content of the oligosaccharide contained in the layers is preferably at the same ratio. In addition, the divalent metallic salt may be contained in any of the ink receiving layers, or it may be contained in some of the ink receiving layers. Furthermore, the coated ink receiving layer may be finished, using a calender such as a machine calender, TG calender, super calender, soft calender, or the like.
The recording sheet for an ink jet printer according to the present invention is constructed as described above, and even the construction which provided only the ink receiving layer has satisfactory properties. Additionally, a glossiness adjusting layer may be provided on a surface of an ink receiving layer, for example, using a general specularity drum type cast coater, or the like, in order to obtain increased value. This glossiness adjusting layer has a preferably characteristic in which glossiness as measured by a 60xc2x0 specular glossiness test according to the Japanese Industrial Standard Z8741 is 10 or more. As material of the glossiness adjusting layer, a mixture of materials of binder resin and pigment employed in the above ink receiving layer may be employed as a coating solution.
In order to maintain glossiness, it is preferable that the compounding ratio of the binding resin to the pigment in the glossiness adjusting layer be 5.0 to 50.0% by weight, and more preferably 5.0 to 30.0% by weight. Coating volume in which the glossiness adjusting layer exhibit superior glossiness without impairing the function of the ink receiving layer, is preferably 3.0 to 25.0 g/m2, and is more preferably 5.0 to 15.0 g/m2.
The glossiness adjusting layer in the present invention preferably includes colloidal silica as a pigment component. The glossiness can be optionally adjusted by employing the colloidal silica which consists of different size particles in an appropriate ratio. This glossiness adjusting layer can be adjusted by choosing the composition in an appropriate ratio so that the glossiness of the printed portion can be higher than that of the nonprinted portion, or conversely, can be lower than it.